Reason for 22LR burst firing? + firing pin Q

[William Wallace]

I got an old Mossberg .22LR rifle a while ago. Apparently the last time this thing was fired was 25+ years ago. It came with the warning from the previous owner: "This this will fire 2-3 round bursts for unknown reasons" Great.

I took it apart and gave it a proper cleaning, but honestly, it looked pretty clean to begin with. I started reading that the firing pins can easily break if dry fired, so I looked up the replacement firing pin on Numrich (e-gunparts.com) as well as some other parts. Lo and behold, it looks like the existing firing pin is from a different model. I was also told that this replacement pin was made in a local machine shop back in the 70s and was copied from the existing pin. I guessed that this might have been the problem with the supposed burst firing. It's not that surprising that it was working, as the parts breakdown of all these 60s era Mossberg 22s look to be very similar.

I ordered a bunch of replacement parts online, and got the correct firing pin. I replaced the firing pin and headed to the range to try to load and fire single rounds only. If that succeeded I would load two rounds at a time and fire these one at a time. At the first sign of a two round burst this rifle either heads to the gunsmith or i just start replacing parts.. most likely the former.

Any conceivable reason why this thing would burst fire as described? I haven't experienced it yet, as I haven't actually fired the rifle. Some folks on rimfirecentral said its might be the firing pin or possibly the sear. It figures that I ordered all kinds of parts but didn't order a sear.

The range trip was pretty short, I loaded a single round, verified that it was seated in the chamber correctly, and fired. Nothing. rinse and repeat x 5. Took that round out, and loaded a different brand round and fired.. Nothing.

Took it home and starting digging around... Crud, It turns out that 'business end' of the new pin is quite a bit wider that the old pin.This allows the old pin to cleanly glide over a flat 'shelf' in the chamber as it hurtles toward the rimfire cartridge. The new pin is too thick and mashes into this flat shelf, so its impossible for the pin to hit the cartridge.

Is it normal practice to have to file a firing pin down?

 

[lord1234]

If it ever burst fires again...strip it, take it apart, and throw away the sear. Thats a good way to go to prison.

 

[Supermoto]

Try a new firing pin spring, if that doesn't work, replace the sear and disconnect

 

[TonyDedo]

No, it's not normal to have to file down the firing pin. And it's CERTAINLY not normal for the gun to fire in bursts. The bursts sounds like it could be the result of an overly ambitious trigger job (too much material taken off the sear). No clue about the firing pin. Sounds like you got yourself a real Bubba Special there.

 

[Rcharnitsk]

I had a sears model 25 that would burst fire because the firing pin was a drop too long, just like yours it was machined locally because the original broke